The present invention relates generally to semiconductor die packages and, more particularly, to an exposed die, lead frame based package.
Semiconductor die packaging provides for suitable external electrical connections and protection of a semiconductor die against mechanical and environmental stresses. Continued progress in reduction of the size of the semiconductor dies and increased functionality and complexity of the circuits integrated in the dies require size reduction of the packaging.
Semiconductor dice are commonly packaged for surface mounting by encapsulating one or more semiconductor dice with a mold compound. In a wire bonded semiconductor die package, the semiconductor die may be mounted on a substrate with electrodes of the semiconductor die on the active face of the die opposite from the substrate. Wires are then bonded to the electrodes and to the exposed electrical contacts of the package to provide the internal connections. The substrate may be an electrically conductive lead frame, whose frame members are cut off and discarded during production after applying molding compound to encapsulate the semiconductor die, the internal connections and the exposed electrical contacts from the lead frame.
One type of semiconductor die package is an exposed flag (or paddle) lead frame package in which the flag is exposed to provide for heat dissipation. During encapsulation, the lead frame and mounted semiconductor die are heated to a molding temperature. The mold compound, in a heated molten form, is then molded to encapsulate the die and part of the lead frame. However, the mold compound does not cover an outwardly facing surface of the die flag. Hence, the die flag is exposed through the mold compound to provide improved thermal dissipation of heat generated by the die during operation.
On problem with the above exposed flag packages is that the die flag and the die each have a significantly lower Coefficient of Thermal Expansion (CTE) than that of the mold compound. As a result, during post mold curing of the mold compound the upper region of the package receives a compressive stress and the bottom region of the package receives a tensile stress. These stresses can cause one or more fractures in the die, located in the tensile stress bottom region, thereby compromising the packaged device.